Re: st: RE: what command to keep firms-years with multiple occurrence of only one type of events

[Roberto Ferrer <refp16@gmail.com>]

If I understand correctly, the following should work. Just -sort-,
compare first event with last event and keep the event that interests
you.

*-------------------------- begin example --------------------------------------
clear
input str2 firm year event
A        1994       2
A        1994       3
A        1994       3
A        1995       1
A         1995      3
A         1996       2
A         1996       4
A         1996       3
A          1997       3
A           1997      3
A           1998       1
A            1998       1
B         1995      3
B         1996       2
B         1996       4
B         1996       3
end

* what you want
sort firm year event
by firm year: keep if event[1] == event[_N] & event == 3

*----------------------- end example -------------------------------------------

On Fri, Sep 27, 2013 at 2:39 PM, Robert Picard <picard@netbox.com> wrote:
> Another way:
>
> bys Firm Year (Event): keep if (Event[1]==Event[_N]) & Event==3
>
> Robert
>
> On Fri, Sep 27, 2013 at 9:29 AM, Joe Canner <jcanner1@jhmi.edu> wrote:
>> Nahla.
>>
>> If your Event variable is numeric, this should work:
>>
>> . bys Firm Year: egen mn=mean(Event)
>> . bys Firm Year: egen sd=sd(Event)
>> . keep if mn==3 & sd==0
>>
>> This is, admittedly, a little unconventional, but should be pretty efficient.
>>
>> Regards,
>> Joe Canner
>> Johns Hopkins University School of Medicine
>>
>> -----Original Message-----
>> From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Nahla Betelmal
>> Sent: Friday, September 27, 2013 4:43 AM
>> To: statalist@hsphsun2.harvard.edu
>> Subject: st: what command to keep firms-years with multiple occurrence of only one type of events
>>
>> Dear Statalist members,
>>
>> It would be great if you can let me know what command I can use to keep firms-years with multiple occurrence of only one type of events in my data.
>>
>> I have firms-years-events data set. A firm can have multiple entries for the same year if it undertakes certain corporate events . I coded the events as 1,2,3, 4. For example the data looks like this
>>
>>
>> Firm   Year    Event
>> A        1994       2
>> A        1994       3
>> A        1994       3
>> A        1995       1
>> A         1995      3
>> A         1996       2
>> A         1996       4
>> A         1996       3
>> A          1997       3
>> A           1997      3
>> A           1998       1
>> A            1998       1
>> B
>> ..
>>
>>
>> I am only interested in studying firm-years where  only event 3 was undertaken (i.e. keep both entries for year 1997 only). In other words, I want to drop firm years where there are a mix of events shown as multiple entries/observations ( years 1994, 1995, 1996) and multiple unique occurrence of event other than 3 (year 1998).
>>
>> I understand that I can do it on two stages, first drop  firm-years with mix events, then second stage drop years with unique events other than 3.
>>
>> the problem that I  don't know what command should I use to do the first stage ( drop firms-years with multiple entries of multiple events).
>>
>> Thank you in advance, I highly appreciate your kind help
>>
>> Nahla Betelmal
>> *
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